The field of tissue engineering presents an exciting avenue for regenerative therapies by combining biomaterials with living cells. The combination of novel biomaterials (scaffolds) with living cells has yielded some clinical success in the reconstruction of a wide range of functional tissues such as, for example, bone, arteries, and bladders. However, due to inflammatory responses and pathological fibrotic states arising following scaffold biodegradation, a novel tissue engineering methodology, called “cell sheet engineering” that constructs 3-D functional tissues by layering two-dimensional cell sheets without the use of any biodegradable extracellular matrix alternatives, has emerged.
Still, the principal shortcoming of cell sheets is their poor mechanical properties when related to functional applications. Cell sheets contract extensively when removed from culture surfaces resulting in reduced graft sizes. In clinical settings it will be ideal to control the specific graft size and shape for specific applications. In addition, the fragility of cell sheets makes handling difficult. Methods to resolve these problems still remain a significant obstacle in the effective reconstruction of mechanically robust and manipulable 3-D tissues even when scaffold-based technologies are avoided.
As regenerative medicine therapies become more advanced there is an increasing need to develop strategies for the scale up of cell and tissue culture to meet predicted demands. In response, there is interest in the use of automated cell and tissue culture systems, the success of which, being dependent on monitoring and control strategies. There are various culture techniques to generate in vitro 2- and 3-D aggregates in suspension, such as 2-D cell seeding on flat and rigid plastic/glass surfaces, pellet, spheroid and hanging drop culture, scaffolding, liquid overlay, spinner flask and the gyratory rotation technique [4]. However, these methods may be limited by either long cultivation time, formation of unequally-sized aggregates or difficult mechanical accessibility. Consequently they may not be suitable for a standardised, rapid and large scale production of 2-/3-D aggregates in a format needed for high-throughput assays
Manipulating micron and submicron sized particles can be accomplished using an acoustic force, Fa=V<e>k Ã sin (2ky), generated by an acoustic stationary field acting in a thin chamber. V is the volume of the particle, <e> is the average acoustic energy, k=2π/λ is the wave number and Ã is the acoustic contrast factor that depends on the acoustic properties of particles and suspending fluid.
This chamber may be called an “acoustic resonator”. This resonator may comprise an emitting wall and a reflective wall. The standing wave may occur when the thickness of the chamber w and the acoustic wavelength λ are related as shown in the following equation: w=nλ/2 where n is the number of nodes created in the thickness of the chamber. Particles subjected to this force field acoustic variable in thickness, may be pushed to the nodes or antinodes of the standing waves, depending on the acoustic contrast factor Ã, which is a function of the acoustic impedances defined as the product ρici, where ρi and ci are the densities and the sound velocities of the fluid or of the suspended particles.
It would also be interesting to develop techniques of tissue engineering for astronaut needs. In weightlessness conditions in space, cell culture is a challenge because cells in culture medium are wandering inside the reactor and are not naturally directed toward a scaffold or a matrix where the aggregate and further tissue has to growth. Forming an aggregate in weightlessness may further take days.
A need exists for a method allowing rapid formation of 2- and 3-D cell aggregates that would be advantageous over the aforementioned conventional methods of cell culturing.
A need exists to obtain a method allowing the formation of multilayer structures consisting of biological objects such as cells.
Another need exists to obtain a method to generate tissue-mimetic constructs.
Another need exists to obtain improved techniques of tissue engineering.
The present invention aims to meet some or all of the aforementioned needs.